Flaugh in U.S. Pat. No. 4,576,959 discloses that 6-substituted-4-dialkylaminotetrahydrobenz[c,d]indoles and their pharmaceutically acceptable salts are central serotonin agonists, useful for treating depression, obesity, alcoholism, smoking, or senile dementia. Leander in U.S. Pat. No. 4,745,126 further discloses that certain 4-dialkylamino-6-aminocarbonyl-1,3,4,5-tetrahydrobenz[c,d]indoles and their pharmaceutically acceptable acid addition salts are useful in treating anxiety.
It is recognized in the art that it is particularly advantageous that a solid pharmaceutical substance be crystalline, rather than amorphous. Typically, crystalline solids more easily purified, more easily characterized, and more pharmaceutically elegant than solids which are amorphous. This invention provides a crystalline acid addition salt of a particularly preferred compound of Flaugh and of Leander.